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Personal Digital Assistants

A personal digital assistant (PDA) is probably the most commonly used small mobile computing device next to a cellular telephone. PDAs are lightweight and small enough to fit in a pocket, and they run essential applications. PDA is a generic name that applies to a simple digital telephone directory and to more elaborate mobile computing devices that run a spreadsheet, word processor, email, and a variety of customized programs.

All PDAs are small computing devices that contain an operating system, processor, memory, and a port to connect the PDA to peripherals and external computing devices. There are three commonly used operating systems on a PDA: EPOC, Palm OS, and Windows CE. EPOC is used in the Psion product line, Palm OS in the Palm PDAs, and Windows CE on various pocket PC devices.

There is an assortment of processors designed for the PDA market that include the DragonBall processor built by Motorola and used in the Palm PDA. The DragonBall has a 16 MHz clock speed. The StrongARM processor, manufactured by Intel, is another PDA processor used in the Psion product line and some pocket PCs. The StrongARM has a clock speed of 200 MHz. Another competitor in the PDA processor market is the Crusoe processor manufactured by Transmeta, which is also found in some pocket PC PDAs.

Avoid equating a PDA's processing speed with that of a desktop or laptop computer. Some operating systems, such as Windows CE, require more processing than a Palm OS PDA to perform a similar task, and the extra processing power running under Windows CE does not necessarily perform a task any faster than a Palm.

Memory is precious in a PDA. A PDA does not have permanent storage, therefore all the applications and data running in a PDA must reside in memory. PDAs use ROM and RAM. ROM is used to store bundled applications from the factory. These include a word processor, spreadsheet, diary, telephone directory, and other kinds of programs that you expect to find in a PDA. Applications that are not bundled with the PDA, and data for all applications including those that reside in ROM, are stored in RAM.

PDAs use one of three types of RAM: Dynamic RAM (DRAM), Enhanced Data Output (EDO), and Synchronous Dynamic RAM (SDRAM). DRAM is the least expensive RAM.

EDO is found in some PDAs, and SDRAM is very rarely used. Generally the more RAM installed in a computer, the better the computer's performance, but this is not necessarily true with PDAs. The amount of RAM that affects performance depends on the PDA's operating system. Windows CE requires more memory (32MB) to perform basic functions than a Palm (4MB).

Some PDAs have an expansion slot for Compact Flash (CF+) cards that contain components such as a modem, cellular telephone, network card used to connect to a local area network, or additional memory that slips into an expansion slot on the PDA to enhance the PDA's functionality.

PDAs have the same problem as all mobile devices. They need batteries to operate- and they drain batteries quickly. You'll learn more about batteries later in this chapter.

PDAs also don't have a user-friendly keyboard to enter data. Designers attempt to overcome the lack of a keyboard by creating a virtual keyboard on a touch-sensitive screen that requires the user to hunt-and-peck to enter data. Another approach to data entry is to use handwriting recognition software. Software running in the PDA analyzes marks made on a touch-sensitive screen and guesses the character that the user wants to enter. Pocket PCs that run Windows CE can use an autocorrect feature that minimizes errors in handwriting recognition. Palm uses its own brand of shorthand called Graffiti.